The invention relates to a belt pretensioner with a pyrotechnic gas generator and a piston/cylinder unit which may be activated by the generated gases and whose piston is connected with a cable.
These types of belt pretensioners are known in various constructional designs. The gas pressure created by the pyrotechnic gas generator results within milliseconds after its activation via a sensor unit, and subjects the piston and the cable connected to it to very high stresses at the beginning of the pretensioning action. The high gas pressure created by the gas generator acts on the piston and accelerates it in the direction of a piston-catching safety device, thus causing the cable to be jerked in the direction of the piston-catching safety device. Strong forces therefore act on both the piston and the cable during the pretensioning operation.
Similarly high stresses can act on a belt pretensioner in the case of a non-intended heat effect when the supplied energy provokes false activation of the gas generator. This is the case, e.g. in a vehicle fire, or in a bonfire test which simulates the former.
For safety reasons, belt pretensioners have to be so designed that they cannot explode or disintegrate into sharp-edged or heavy flying objects in the case of a non-intended, false detonation of the gas generator, e.g. in a vehicle fire, and also not be damaged by the high stresses occurring at the beginning of the pretensioning operation in the case of a correct operational detonation.